1. Field of the Invention
The invention relates to mechanized rock breaking techniques. More particularly, the invention relates to methods, apparatuses and cartridges for non-explosive rock fragmentation.
2. Description of the Prior Art
Oversized rocks and boulders are a substantial world-wide problem in underground mining, surface mining, open pits and quarries, earth moving and allied construction works, and civil demolition projects. For the purposes of the following specification, the terms rock(s) and boulder(s) are considered to be interchangeable, and the use of the either terms should not be construed as limiting the disclosed invention in any way.
Ideal rock fragmentation processes produce a cost effective and optimum particle size distribution. This requires the production of rock fragments having an average particle size as small as possible to lessen further handling within the mine transportation system and to minimize the necessity for subsequent size reduction. Underground mining operations often produce oversized boulders that are too large to flow naturally from the ore draw points and ore passes. Additionally, the oversized boulders may be too large for loading and transport equipment. The boulders may also be too large for primary crushing and must be further reduced in size before they are crushed.
These large boulders are often created by inaccurate drilling of blast holes for explosives, misfiring of explosives, using the wrong explosives, and incorrect planning of hole patterns. The large boulders must be reduced in size by secondary size reduction, before they can be removed from the project site. Additionally, some mining methods, such as block caving, have a natural tendency to generate large boulders that must be individually reduced in size on an on-going daily basis. Underground mining operations also confront large slabs or boulders that may cave-in as an undesirable by-product of mined ore boundaries. These large slabs and boulders must also be dealt with in secondary rock breaking operations.
Three methods are commonly employed in underground operations for secondary size reduction. According to a first method (drill and blast method), a single hole or several holes are drilled in the oversized boulder, explosives are installed in the hole and the boulder is blasted into smaller fragments. A second method employs directional explosives (shaped charges). The directional explosives are simply attached to the rock surface and set off. This method either breaks the rock or, if the rock is stuck in a draw point, brings the rock onto the loading level where it is reduced by the drill and blast method or removed by loading equipment. A third method employs pneumatic or hydraulic impact hammers to split the rock into smaller fragments. This method is very time consuming, requires substantial man hours, and utilizes expensive and heavy equipment.
The use of explosives in the drill and blast method and the shaped charge method present inherent problems. These problems include, the necessity for the evacuation of the mining personnel and equipment from the blast area prior to the blast, the need to schedule the blast, and the requirement that the blast area be ventilated for a period of time before personnel are allowed back into the working area to continue their work. Additionally, the use of explosives require personnel qualified to handle and work with explosives. Further, the cost of secondary blasting is high relative to the general cost-per-ton mined and the activity is very time consuming per unit volume of rock broken. Also, the use of explosives often causes damage to the surrounding rock and nearby secondary structures. Finally, the use of explosives or shaped charges presents an exceptional safety risk when the work is conducted in conditions where the rock is hanging over-head (so called hang ups).
Oversized boulders are also commonly created in surface mining and quarrying due to inaccurate drilling or charging of blast holes, misfiring of the explosives during the blast, using the wrong explosives and misjudging the hole-pattern planning. Two main methods are commonly employed in surface operations for secondary size reduction. The first method is the drill and blast method discussed above. Surface operations and quarrying also utilize pneumatic and hydraulic impact hammers to split oversized boulders into smaller fragments. These methods present problems similar to those encountered during secondary size reduction in underground operations.
During earth moving and building construction, large rocks which can not be handled by loading and transport equipment are occasionally hit. These rocks are normally reduced through the use of explosives. As with underground and surface mining, the use of explosives presents a wide range of problems. The use of explosives in earth moving and building construction presents additional problems when the blast is conducted in urban areas, because there is always potential liability from flying rocks and blast vibration damage to surrounding structures and equipment.
The explosive methods for secondary size reduction discussed above may be replaced by non-explosive propellant base techniques. These techniques are safer, but they are highly time consuming due do the manual work required to install the shooting devices, cartridges, and absorbing mats. Current non-explosive techniques are relatively unsafe due to the manual charging of the charging device. U.S. Pat. No. 4,900,092 to Van Der Westhuizen et al. discloses such a propellant based technique.
In addition to dealing effectively with oversized boulder in mining and excavation processes, breaking up and excavating an original mass of rock efficiently is a major mining concern. To this end, numerous developments over the years have been advanced in order to both enhance excavation process rates and create safer work environments. A third important factor in new development efforts has focused on developing technologies and techniques that allow rock excavation processes to be performed on a continuous basis.
A method for rock breaking which satisfies the ability to break very hard rock with energy efficiency and excavate the broken rock on a continuous basis, employs non-explosive propellant based techniques. This method is performed in the following manner: drilling a short hole in a monolithic rock structure, wherein the hole is stepped narrower at the bottom few inches of the hole; inserting the barrel of a military-type cannon into the hole and forcing it to the bottom of the hole to create a mechanical seal by the forward force applied to the gun barrel against the rock shoulder; firing a propellant based cartridge in the barrel of the cannon to pressurize the bottom of the hole and cause a small volume of rock to break out of the massive structure. Alternately, the propellant-based cartridge can be placed on the end of a charging bar and the charging bar can be forced within the hole to place the cartridge at the bottom of the hole. The force of the charging bar against the shoulder of the stepped hole creates a seal. Once the cartridge is properly positioned and the seal is created, the cartridge may be fired and ignited to destroy the rock.
Non-explosive techniques are disclosed in U.S. Pat. No. 5,308,149, to Watson et al., and U.S. Pat. No. 5,098,163, to Young, III. The techniques disclosed by Watson et al. and Young, III, are relatively safe, but require highly sophisticated, vulnerable and expensive equipment. Additionally, due to the non-standard nature of the propellant cartridges (cartridge cost) these techniques are costly to operate.
As discussed above, prior rock breaking techniques are limited in their effectiveness. Specifically, drill and blast techniques are the most common methods employed, but they are expensive, unsafe, time consuming and hazardous to the surroundings. Directional explosives are also common, but they are not efficient and are unsafe as a result of the explosives involved. Non-explosive propellant based techniques, such as those disclosed in U.S. Pat. No. 4,900,092, are relatively safe, but highly time consuming due to the manual work required to install the shooting device, cartridges, and absorbing mat.
In addition, high pressure water methods (without explosives) require high water pressure and high impulse speed in order to overcome the inherent strength of the rock. Generating sufficient water pressure and impulse speed requires complicated and expensive pump devices and components. Further, high water pressure methods demand extreme water purity standards in order to operate successfully. These devices also have very high maintenance costs associated with their operation, particularly in the dirty and harsh environments of mining, quarrying and construction.
The non-explosive techniques disclosed in U.S. Pat. Nos. 5,308,149 and 5,098,163 are relatively safe, but require highly sophisticate and expensive equipment. Consequently, they are costly to operate. Additionally, these non-explosive techniques present noise problems when misfires occur. The technology also requires a large, heavy, complicated and expensive military-like cannon, which is expensive to maintain. In order to operate these cannon-type rock breaking devices, the following gun components are essential: a strong heavy duty barrel able to withstand the firing shock and stress of falling rocks; a recoil dampening mechanism to protect the gun, its components, and the equipment it is integrated with; and an accurate loading and storage device for the cartridges.
These cannons also create undesirable dangers. Specifically, the cannons are potentially unsafe, since reloading is done closer to the face. Additionally, the gun barrel is in the drill hole within the rock structure and as such is exposed to rock damage after the cartridge is fired. Further, the gun components are large and heavy, and require heavy structures to support the weight and recoil forces associated with the propellant pressure impact. These conditions cause a cumulative demand for heavier non-conventional booms to carry the extra gun components, the heavier booms require heavier non-conventional carriers, all of which result in very high capital costs. In summary, these heavy, large, complicated and expensive systems are severely limit in the applications where they can be employed, and are generally only suitable for large mining or construction applications.
After studying methods and apparatuses currently available for rock breaking operations, it is apparent that a need exists for an efficient, safe, and cost effective method, apparatus and cartridge for rock breaking operations. The present invention provides such a method and apparatus.